The Suzaku Observations of SS Cygni in Quiescence and Outburst

TL;DR

This study uses Suzaku X-ray observations to analyze the plasma properties, elemental abundances, and reflection features of SS Cygni during quiescence and outburst, revealing significant differences in plasma temperature and reflection geometry.

Contribution

First detailed Suzaku X-ray spectral analysis of SS Cygni in both quiescence and outburst states, providing new insights into plasma parameters and reflection mechanisms.

Findings

Plasma temperature is higher in quiescence (20.4 keV) than in outburst (6.0 keV).

Elemental abundances are near solar for medium-Z elements, but oxygen and iron are subsolar, with carbon notably high.

Reflection features indicate different accretion geometries in quiescence and outburst, involving the white dwarf, accretion disk, and equatorial belt.

Abstract

We present results from the Suzaku observations of the dwarf nova SS Cyg in quiescence and outburst in 2005 November. Owing to high sensitivity of the HXD PIN detector and high spectral resolution of the XIS, we have determined parameters of the plasma with unprecedented precision. The maximum temperature of the plasma in quiescence 20.4 +4.0-2.6 (stat.) +/- 3.0 (sys.) keV is significantly higher than that in outburst 6.0 +0.2-1.3 keV. The elemental abundances are close to the solar ones for the medium-Z elements (Si, S, Ar) whereas they decline both in lighter and heavier elements. Those of oxygen and iron are 0.46 and 0.37 solar, respectively. That of carbon is exceptionally high and 2 solar at least. The solid angle of the reflector subtending over the optically thin thermal plasma is Omega/2\pi = 1.7+/-0.2 (stat.) +/-0.1 (sys.) in quiescence. A 6.4 keV iron Ka line is resolved into a narrow and broad components. These facts indicate that both the white dwarf and the accretion disk contribute to the continuum reflection and the 6.4 keV iron Ka line. We consider the standard optically thin boundary layer as the most plausible picture for the plasma configuration in quiescence. The solid angle of the reflector in outburst Omega/2\pi = 0.9 +0.5-0.4 and a broad 6.4 keV iron line indicates that the reflection in outburst originates from the accretion disk and an equatorial accretion belt. From the energy width of the 6.4 keV line, we consider the optically thin thermal plasma in outburst as being distributed on the accretion disk like solar coronae.